Other water companies charge in the same way, so without a water meter your current bill will be based on your home’s rateable value – a fixed assessment made some time between 1973 and 1990, and taking into account features such as the size of your home.

Metered customers on the other hand are charged according to their water usage.

Joe Payne from the Energy Saving Trust (EST) said: "In general, switching to a water meter will have the greatest financial benefit to smaller families in larger homes with higher rateable value. Since ST's household is larger than average (two to three people) it is perhaps unsurprising that her water use is slightly higher."

As a result, the best way for ST to reduce her water bills is by switching to a meter.

However, it is possible for unmetered customers to reduce electricity and gas bills by being more careful with their water use. "Around 21pc of a gas heated household’s heating bill is used to heat water for baths, showers and hot water from the tap, and so saving water can also save energy," Mr Payne added.

Households in England and Wales can ask their water company to install a water meter free of charge.

For households on a meter and looking for ways to cut their water bills, the bathroom is the best place to start. According to a report last year from the Energy Saving Trust, showers were found to be the biggest consumers of water in the home, using a quarter of the total.

Home owners can replace an inefficient shower head with a water efficient one, which could save a four-person household £65 on their gas bills, the EST said. A home paying on a water meter could save a further £95 on their water bills.

If you speak to your water provider it could provide you with water efficient shower-heads, and other useful water-saving kit, for free or at a discounted rate.

Although advice like "turn the tap off while brushing your teeth" is obvious, don't underestimate just how much you could save by following tips like these.

A running tap wastes more than nine litres of water a minute, says Ofwat, the regulator, and this can slowly add up to a significant amount of water use. More tips on cutting your water bill can be found here.

Also, for those not on a meter, try the Consumer Council for Water’s online Water Meter Calculator to see if you might be able to save money by switching.

Do you have a question for our experts? Email us at moneyexpert@telegraph.co.uk